Plastic extrusion apparatus



Feb. 10, 1970 L R, ALBERT ET AL PLAST-Ic EXTRUSION APPARATUS u 4Sheets-Sheet 1 Original Filed Aug. 27, 1 965 TTORNKS.

Feb-10,. 1970 '.1. R. ALBERT ETAL 3,493,9'97

' PLASTIC ExTRUsIoN APPARATUS 4 Sheets-Sheet 2 Original- Filed Aug. 27,1965 ATZNEKS s A A A\\\\ Feb. 1o, 1970 J. R, ALBERT ET A.. 3,493,997

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ATTORNEYS.

United States Patent O 3,493,997 PLASTIC EXTRUSION APPARATUS John R.Albert, Leawood, and Michael J. Grebowiec, Shawnee Mission, Kans.,assignors to Brockway Glass Company, Inc., Brockway, Pa.

Original application Aug. 27, 1965, Ser. No. 483,204, now Patent No.3,417,432. Divided and this application Apr. 15, 1968, Ser. No. 763,436

Int. Cl. B29d 23/04 U.S. Cl. 18-14 5 Claims ABSTRACT OF THE DISCLOSUREThis disclosure relates to improvements in the process of blow moldingplastic to provide increased eiliciency of operation of the moldingapparatus, reduce operational and maintenance costs, eliminateunnecessary downtime caused by apparatus malfunctioning, and provide anirnproved plastic product having greater strength and durability.

This application is a division of application Ser. No. 483,204, 4filedAug. 27, 1965 and now U.S. Patent No. 3,417,432.

Machines for blow molding plastic commonly employ an extruder foradmixing the plastic material and any pigment that is to be utilized togive the molded product a desired color. To assure uniform pigmentationand produce a homogeneous plastic mass for molding, it has been thepractice to provide an extruder tip having sets of teeth which areshifted relative to one another while in contact with the plastic massto thereby effect the mixing function. Although this approach has provensatisfactory, problems frequently occur when a back pressure builds upin the plastic distribution lines which lead to the molding stations.Under such conditions, the pressure transmitted back to the extruder tipexerts a substantial force thereon which can cause shifting of themoving parts of the tip in their bearings and produce undesiredtooth-totooth contact, resulting in shearing of the teeth and permanentdamage necessitating complete shutdown of the apparatus for repairs.

It is, therefore, an object of this invention to provide a homogenizerfor use with plastic blow molding apparatus which will not be subject tothe above-mentioned tooth intermeshing problem under high back pressureconditions.

As a corollary to the above, it is another object of the instantinvention to provide such a homogenizer which is constructed andarranged to respond to high back pressures in a manner which assures themaintenance of desired clearance between the material mixing teeththereof.

Still another object of the invention is to provide a homogenizer asaforesaid which will subject the plastic or other material to shearingstresses and simultaneously compress the material into a homogenousmass.

Besides the provision of improved means for homogenizing the plasticmaterial prior to blow molding thereof, the instant invention is alsodirected to an improved plastic molding station which forms the plasticin a manner to eliminate the line of weakness in the molded productwhich is produced by conventional molding methods. In apparatus of theart, the plastic is formed into a tube by a molding head and permittedto gravitate around a mandrel guide to a position between a pair ofmolding dies, whereupon air under pressure is introduced into one end ofthe tube to expand the latter in the die. Since only a single plastictube is formed by the molding head, a weld lin'e or seam is necessarilyproduced extending l-ongitudinally of the tube, resulting in thepresence of a line of weakness in the finished product after expansionin the molding die.

ICC

It is, therefore, another object of the instant invention to provide amethod and apparatus for producing a pair of concentric, tubularsheaths, having individual, nonaligned weld lines, which are combined toform a composite tube prior to entry into the die.

A further object of the invention is to provide a molding station havingan upper and a lower molding head which discharge respective sheaths inconcentric relationship to one another through coaxial annular openings.

Still another object of this invention is to provide a pair of moldingheads as aforesaid which are disposed in opposed relationship to oneanother and have a divider therebetween for splitting the incomingplastic into a pair of streams and directing said streams to respectiveheads.

Other aims of the instant invention are to provide an improved valve forcontrolling plastic flow to a molding station; to provide a ball jointconnection between the main plastic supply line and each secondary lineleading to a molding station; to provide novel means for centering themandrel in the molding station; and to provide a safety valve forrelieving excessive back pressure at the homogenizer outlet.

With reference to the above-mentioned plastic control valve, it isnoteworthy that a specific object of this invention is to provide such avalve that will not foul the bushings or bearings utilized to journalthe valve operating shaft in the valve body when leakage occurs aroundthe valve member. This will occur due to the pressure in the plasticdistribution lines. Thus. it is an additional object of the invention toprovide a means for recovering the leakage free from contamination bythe valve bushings or bearings and, therefore, in a condition forsubsequent reuse without waste.

In the drawings:

FIGURE l is a diagrammatic illustration of the cornplete blow moldingapparatus;

FIG. 2 is a central, vertical sectional view of the homogenizer;

FIG. 3 is a top plan view of the homogenizer housing;

FIG. 4 is a fragmentary, detailed, elevational view of the female partof the homogenizer;

FIG. 5 is a detailed, elevational view of the male part of thehomogenizer;

FIG. 6 is a fragmentary, central, horizontal section showing a balljoint connection between the main plastic distribution line and asecondary line;

FIG. 7 is a front, elevational view of one of the molding stations;

FIG. 8 is a central, vertical sectional view showing the plastic flowcontrol valve and the tube forming portion of the molding station;

FIG. 9 is a horizontal sectional view taken along line 9-9 of FIG. 8,the divider ring being removed and certain components shown in plan forclarity;

FIG. 10 is a detailed, bottom view of the upper molding head;

FIG. 1l is a vertical sectional view of the plastic control valvelooking toward the molding station or rightwardly as viewed in FIGS. `8and 9;

FIG. l2 is a plan view of the lower plate and centering ring of themolding station;

FIG. 13 is a cross-sectional view of the plastic tube formed by themolding heads and the mandrel; and

FIG. 14 is a schematic diagram of the pneumatic and hydraulic controlsystem of the apparatus.

THE HOMOGENIZER, SAFETY VALVE AND DISTRIBUTION SYSTEM Referring to FIG.l, the numeral'20` denotes a conventional extruder utilized in plasticblow molding, such extruder being provided with a hopper 22 forreceiving plastic pellets or the like. The extruder contains heatingmeans which subjects the solid pellets to suicient heat to convert thesame to the fluid state so that a owing plastic mass is formed withinthe extruder. Pigment iS also introduced into hopper 22 to give theplastic a desired color.

The heated plastic mass is fed to a homogenizer 24 which thoroughlyadmixes the plastic and the pigment prior to feeding of the same underpressure to a pair of main distribution lines 26 and 28. Main line 26 ispro vided with a pair of ball joint connections 30` and 32 coupling thesame with secondary lines 34 and 36. The secondary lines 34 and 36 leadto molding stations 38 and 40 respectively. The end of line 26 remotefrom homogenizer 24 is directly connected with a third molding station42 by a ball joint connection 44.

A similar arrangement exists for main line 28, the latter being coupledwith a pair of secondary lines 46 and 48 by ball joint connections 50and 52 respectively. Secondary lines 46 and 48 feed molding stations 54and 56, the end of line 218 remote from homogenizer 24- being directlyconnected to a molding station 58 -by ball joint connection 60. A safetyrelief valve 62 is shown coupled to homogenizer 24 at the junction ofmain lines 26 and 28, such valve being employed to relieve back pressureat the homogenizer should the same reach an excessive value.

Homogenizer 24 is shown in detail in FIG. 2. A tube 64 extending fromthe housing of extruder 20 is joined to a block 66 which forms thehousing of homogenizer 24. Tube 64 is provided with a bore 68 whichextends longitudinally of extruder beneath hopper 22 and receives theplastic and the pigment fed into the hopper, While in bore `68 theplastic is subjected to heat and slowly advanced along the bore by arotating auger 70. A tapered element 72 is threaded into the auger shaftand axially therewith to present a cone-like tip extending from the endof the auger.

An insert 74 in block 65 abuts tube 64 and has a generally frustoconicalopening therethrough receiving element 72 to form a material passage 76communicating bore 468 with a bore 78 in block 66. Bore 78 is of lesserdiameter than bore 68 and is coaxially aligned therewith to form acontinuation of bore `68 after passage of material through therestriction presented by insert 74.

It will be appreciated that element 72 and insert 74 form, respectively,the male and female parts of the homogenizer, insert 74 being providedwith three circular rows of teeth y80', 82 and 84 in concentricalignment and axially spaced, as shown in FIG. 2. Teeth 80` are eighteenin number, there being sixteen teeth 82 and ten teeth 84. Similarly,element 72 is provided with three rows of external teeth |86, 88 and 90,numbering 18, 16 and 10 respectively.

In FIG. 2 it may be seen that the teeth 86 of element 72 presentVertical surfaces 92 lying in a common plane extending orthogonally ofthe common axis of bores 68 and 78. Similarly, the teeth 82 of insert 74present vertical surfaces 94 lying in a common plane extendingorthogonally of the common axis of the bores. Thus, when the opposedteeth 86 and 82 are in alignment as illustrated, the passage 76therebetween is narrowed to a short, vertical stretch defined by thesurfaces 92 and 94 of the opposed teeth.

Teeth 88 and y84 of element 72 and insert 74 are like- Wise arranged andpresent vertical surfaces 96 and 98, respectively. It will beappreciated, however, that the horizontally opposing teeth of element 72and insert 74 are unequal in number so that, as shown, the variousvertical surfaces will not simultaneously move into direct opposition.For example, the particular surfaces 96 and 98 shown in FIG. 2 are notin direct opposition since the two pairs of teeth 84 and 86 there shownare revealed in elevation.

Bore 78 feeds material from the homogenizer into a pair of branchpassages 100 and 102 (FIGS. 2 and 3) which communicate with main lines26 and 28, respectively. Safety relief valve 62 includes a pin 104slidably received in an opening 106 communicating with bore 718 betweenbranch passages and 102. A relief hole 108 extends upwardly from theunderside of block 66 and intersects opening 106, the hole beingnormally blocked by the presence of pin 104.

Pin 104 is provided with a head 110 which bears against the endpiece 112of an arm 114. A pivot pin 116 is rigid in endpiece 112 and pivotallymounts arm 114 for swinging movement in a counterclockwise direction (asviewed in FIG. 2) upon rightward movement of pin 104. A weight 118 iscoupled with the outer end 120 of arm 114 to normally maintain the armand the pin in the positions shown.

It will be appreciated that pin 104 and its associated structure operatewhen the back pressure in bore 78 reaches a predetermined maximum valuedetermined by the mass of Weight 118. When pin 104 shifts a sufficientdistance to the right, as viewed in FIG. 2, relief hole 108 is opened topermit ydischarge of plastic from bore 78 to relieve the excessivepressure therein.

Referring to FIG. 6, one of the ball joint connections 30 is there shownin detail. It should be understood that the other connections 32, 44,50, 52 and r60 utilized in the system are identical to that as shown inFIG. 6.

Secondary line 34 is provided with a block 122 at the end thereofadjacent main line 26, block 122 having a central passage 124 thereincommunicating with the secondary line and intersecting a central passage126 in a block 128 interposed in main line 26. Passage 126 registerswith the main line as illustrated, it being evident that neither of theblocks 122 nor 126 impede the flow of material through the respectivelines.

Block 122 presents a flat face 130 having a domeshaped projection 132thereon presenting a convex, spherical surface which is received by amating recess in face 134 of block 128. `Cap screws 136 extend throughblock 128 and are threadably received by tapped holes in block 122 sothat, upon tightening of screws 136, faces 130 and 134 are drawn towardone another. It is evident that loosening of screws 136 permits amovement of secondary line 34 to adjust the same to the particulardisposition of its associated molding station 38 to facilitate thelayout of the various subassemblies of the apparatus. Subsequenttightening of the screws seats the arcuate mating surfaces to form aleak-free connection.

THE MOLDING STATION Referring to FIG. 7, the molding station 38illustrated diagrammatically in FIG. l is shown in front elevation, itbeing understood that the other molding stations are identical inconstruction and function. A base 138 is provided with a pair ofaligned, horizontal tracks 140 which carry slide blocks 142 rigid with apair of opposed die sections 144. A pair of linkages 146 are pivotallycoupled with respective slide blocks 142, the ends of linkages remotefor the slide blocks being pivotally connected to adjustable endsupports 148. A pair of double-acting pneumatic cylinders 150 extendfrom the sides of base 138 as shown and operate to move the die sections144 toward and away from one another. The footing of base 138 is notshown.

A mandrel and molding head housing 152 is disposed above die sections144 and is provided with a lower plate 154. A valve body 156 is securedto the left side of housing 152 and has an operating shaft 158projecting forwardly therefrom. A crank 160 is connected to shaft 158,crank 160 being operably coupled with a double-acting pneumatic cylinder1'62 by a piston lro-d 164. Cylinder 162 is suspended from -framework166, the latter and valve body 156 being supported in part by an uprightbrace 168.

An arm is pivotally connected to crank 160 at one end thereof, the otherend of the arm being provided with a cam 172 which rides over an idler174. Cam 172 is disposed to engage the actuator 176 of solenoid-operatedhydraulic valve 178 which controls the flow of hydraulic uid to adouble-acting hydraulic cylinder 180 carried by a bracket 182 rigid withand extending laterally from housing 152. The piston rod 184 of cylinder180 has its free end rigidly secured to an end plate 186 forming a partof bracket 182.

The cylinder 180 carries a cam 188 which is engageable with a camfollower 190 depending from a lever arm 192 haivng a fulcrum at 194. Theupper extremity of a man1 drel 196 is visible in FIG. 7 between bracket182 and the left end of lever arm 192, the latter being pivotally compled with mandrel 196 at the upper extremity thereof for communicatingthe mandrel with a source (not shown) of air under pressure during theLblow molding operation. The end of the secondary line 34 may be seencommunicating with valve body 156 at the left side thereof.

FIGS. 8-12 show the portions of the molding station of interest indetail. Mandrel 196 is reciprocably mounted in the central bore of amandrel guide 202 threaded into the top of housing 152. Mandrel guide202 extends downwardly through housing 152 in the form of a cylinder 204of reduced diameter having a tapered, lower end. An upper molding head206 :receives cylinder 204 and is seated between the cylinder and thehousing 152. A lower mold` ing head 208 is also seated in the housingbelow the upper head 206 and above the lower extremity of the cylinder204.

Mandrel 196 has a tape-red, lower extremity 210 which, in the positionshown, projects through an orice 212 in the bottom of a receiver 214.Receiver 214 has a conical passage 21'6 therethrough receiving extremity210 and is provided with an annular ange 218 which overlies an annularshoulder formed in lower plate 154. A centering `.ring 220 surroundsange 218 and is utilized to center the mandrel in a manner to beexplained hereinafter. A bi- -furcated paddle 222 is disposed beneathlower plate 154 and is vertically reciprocable by a single-actingpneumatic cylinder 224 (FIG. 14) to dislodge the molded product afterthe blow molding operation.

The upper head 206 presents a horizontal face 226 and has a depending,cylindrical neck 228'. A flow channel o1 groove 230 comprising a pair ofsegments 232 and 234 separated by a `web or stop 236. The ends 230 ofchannel 230 communicate with a beveled edge 240 of head 206, edge 240being registered with a gate 242 which, in turn, is in iluidcommunication with a passage 244 in valve body 156.

A divider ring 246 is clamped between heads 206 and 208 as shown in FIG.8 and is provided with a depending annular ange 248. Divider ring 246serves to split the stream of fluid plastic entering the heads from gate242 and provide a pair of ow paths for the plastic to the respectivemolding heads. It should be noted that both of the heads are generallycylindrical in configuration and that channel 230 of head 206substantially encircles neck 228 in concentric relationship thereto.

In like fashion, the lower mol-ding head 208 presents a horizontal face250 having a flow channel 252 or groove therein divided into a pair ofsegments 254 and 256 by a web or a stop 258. The ends 260 of channel 252communicate 4with a beveled edge 262 of head 208, edge 262, in turn,being in fluid communication with gate 242. An air passage 264 extendsaxially through mandrel 196 and communicates at its upper end with airline 200 (FIG. 7).

Lower head 208 has a central, circular aperture 26'6 extendingdownwardly therethrough which forms a tubular passage for plastic owaround neck 228 and the lower, cylindrical portion 204 of mandrel guide202. (For clarity of illustration, both the divider ring 246 and theupper head 206 are removed from the sectional view of FIG. 9.) The neck228 of upper head 206 and the flange 248 of -ring 246 define an annularopening 268 for passage of plastic from the upper head downwardly alongcylinder 204. Thus it will be appreciated that the annular opening 268and the annular aperture 266 form concentric ow paths for the plastic asthe same is discharged from the flow channels of the heads. It isnoteworthy that approximately one-fourth to one-third of the annularange 248 is of reduced width, this reduced portion being located on theright-hand side of neck 228 as viewed on FIG. 8. Additionally, it shouldbe understood that the heads 206 and 208 are disposed with their channelstops 236 and 258 located in diametric opposition to one another.

In FIG. l2, the centering ring 220 is shown in detail. The ring has aslot 270 therein which receives an upstanding pin 272 rigid with plate154. Ring 220 is provided with an extension 274 opposite slot 270 whichprojects radially outwardly from the ring through a groove 276 in plate154. A U-shaped member 278 carries a pair 0f cap screws 280 which extendtoward one another into engagement with opposed sides of extension 274.A threaded adjusting device 282 is also received by member 278 and iscoupled with the end of extension 274 by a tongue and groove coupling.It will be appreciated that adjustment of screws 280 will shift ring 220from side-toside, while threading of device 282 will effectfront-to-back movement of the centering ring. Sufficient play is left inthe tongue and groove coupling of device 282 with extension 274 topermit lateral movement of ring 220 by screws 280 without binding. Inthis manner, mandrel 196 may be centered with respect to receiver 214 toproperly align orice 212 with the lowermost extremity 210 of themandrel.

Referring particularly to FIGS. 8, 9 and 11, it may be seen that valvebody 156 is provided with a horizontal bore 284 therethrough having avalve member or spool 286 disposed therein to form a chamber 288 at thecentral portion of bore 284. An inlet port 290 and an outlet port 292communicate with opposed sides of chamber 288, upon operation of valvemember 286 to open the valve, these ports place secondary line 34 influid communication with passage 244.

Operating shaft 158 is integral with one end of spool 286, a secondshaft 294 being rigid with the other end of the spool and extendingtherefrom in opposition to shaft 158. A bearing housing 296 having aretaining plate 298 is mounted on body 156 and contains a pair of needlebearings 300 which journal shaft 294 in bore 284. A needle bearing 302serves to journal shaft 158 in bore 284.

Spool 286 comprises a pair of spaced-apart end discs 304 which arereceived in bore 284 as shown. A central web 306 is integral with discs304 and connects the same, said web extending along a diameter of thespool and presenting opposed flow surfaces 308 which converge t0- wardone another as the ends of the diameter are approached, as is clearlyillustrated in FIG. 8.

A pair of primary sealing rings 310 abut the end faces of respectivediscs 304 and are seated within bore 284, the circumferential peripheryof each of the rings 310 being in tight, sealing engagement with thebore. The internal circular surfaces of the rings 310 are in radiallyspaced relationship to respective shafts 294 and 158 to define annularcavities 312. A pair of secondary sealing rings 314 abut the outer,annular surfaces of respective rings 310 and are in tight engagementwith shafts 294 and 158, respectively. A pair of annular grooves 316 aredefined by body 156 and the needle bearings 300 and 302 adjacent spool286, such grooves receiving secondary sealing rings 314 and leaving anannular space between the circumferential periphery of each ring 314 andthe valve body.

A relief passage 318 extends axially of shaft 158 and has a right-anglebend communicating with the cavity 312 of its associated primary sealingring 310. Similarly, shaft 294 has a relief passage 320 extendingaxially thereof, registering with an opening 322 in plate 298 and havinga right-angle bend communicating with the cavity 312 of its associatedsealing ring 310.

Valve body 156 is provided with a pair of relief passages 324 whichcommunicate with respective annular grooves 316 surrounding thesecondary sealing rings 314. Thus, any plastic which leaks around thevalve spool 286 is prevented from fouling the bearings 300 or 302 due tothe relief afforded by passages 318, 320 and 324. It should be notedthat primary rings 310 are composed of a material having a highercoeicient of expansion than the surrounding valve components so that, inthe presence of the heated plastic, rings 310 expand and form a tightseal with bore 284. Rings 310 may, for example, lbe composed of copperwhile the remainder of the valve comprises steel alloy parts.

THE APPARATUS CONTROL SYSTEM FIGURE 14 illustrates a suitable controlsystem for controlling the operation of one of the plastic blow moldingstations. It should be understood that six such control systems would beemployed in the apparatus shown since six molding stations are utilized.

A timer motor 326 drives seven timing discs 328, 330, 332, 334, 336, 338and 340 which are provided with cam surfaces relatively disposed in therelationship indicated. Motor 326 drives the timing discs 328-340 in aclockwise direction to sequentially place their cam surfaces intoengagement with the actuator arms of cam switches 342, 344, 346, 348,350, 352 and 354, respectively. Switch 342 controls the energization ofthe solenoid 356 coupled with a valve 358; switch 344 controls theenergization of a solenoid 360 operably coupled with a valve 362; switch346 is connected to a pair of solenoids 364 and 366 which are, in turn,coupled with respective valves 368 and 370; switch 348 controls theenergization of a solenoid 372 which operates a valve 374; switch 350 isoperably coupled with a solenoid 376 which controls valve 378; switch352 is electrically connected to a pair of solenoids 380 and 382operably coupled with respective valve 384 and 386; and switch 354 isconnected with a solenoid 388 which operates valve 390. A suitablesource of electrical power (not shown) is connected to terminals 392 ofswitches 342-354 to provide the operating current for the varioussolenoids.

An air line 394 is in communication with a source (not shown) of airunder pressure, line 394 being provided with four branch lines 396, 398,400 and 402. Valves 358 and 362 are interposed in lines 396 and 398,respectively, which are connected to cylinder 162 for operating thelatter. Valve 374 is interposed in series with branch line 400 tocontrol air ilow therethrough to mandrel 196, valve 370 Abeing disposedin an exhaust line 404 communicating with branch line 400 between valve374 and mandrel 196. Valves 368 and 384 control the flow of air underpressure from branch line 402 to the lefthand pneumatic cylinder 150which operates the left-hand die section 144, while the two valves 336and 370 control air flow to the righthand pneumatic cylinder 150. Thetwo cylinders 150 are each provided with piston rods 151 operablycoupled with respective die sections 144. Valve 390 is in main line 394at the end thereof and controls passage of air to cylinder 224, thelatter effecting vertical reciprocation of paddle 22 via its associatedpiston rod 225. Each of the pneumatic valves shown in FIG. 14 is closedwhen its solenoid is de-energized, and thus normally blocks the passageof air in the associated line. Additionally, it should be understoodthat each of the valves 358, 362, 368, 384, 386, 370 and 390 is providedwith an exhaust port 408 which relieves the pressure in the associatedcylinder when the valve is in the open condition.

A hydraulic fluid source (not shown) is coupled with hydraulic valve 178via inlet line 410. The return line of the hydraulic system is incommunication wtih outlet 412 of valve 178. Lines 414 and 416communicate the control ports of the valve with cylinder 180. Valve 178is a conventional device designed to communicate inlet line 410 withline 414, and simultaneously communicate line 416 with outlet 412, whenthe valve is in one mode of operation. Alternatively, in its otheroperational mode, valve 178 communicates inlet line 410 with line 416and simultaneously communicates line 414 with the outlet 412. Valve 178normally is in the rst operational mode above described to maintainpiston rod 184 extended, as illustrated in FIG. 7.

OPERATION As explained earlier, plastic in pellet form is loaded intohopper 22 for heating by the extruder 20. Such plastic may take the formof any suitable synthetic resin capable of being converted into the uidstate upon heating thereof, and subsequently returned to the solid stateupon cooling. Power means (not shown) drives auger 70 to force the uidplastic mass into the homogenizer 24.

The homogenizer kneads the plastic material and thoroughly mixes thesame with the pigment which is also introduced into the hopper. Therestriction in the bore 68, 78 serves to compress the plastic mass whilesimultaneously subjecting the plastic to shearing stress by the actionof the homogenizer teeth. It should be appreciated that, shouldexcessive back pressure develop in bore 78 prior to opening of reliefvalve 62, the male and female parts 72 and 74 of the homogenizer willnot be forced into engagement with one another because pressure againstthe nose of the male part or element 72 tends to increase the spacingbetween the opposed teeth rather than force the same into damagingengagement.

The fluid plastic is distributed through lines 26 and 28 and thesecondary lines to the various molding stations as illustrated inFIG. 1. The molding stations are op erated sequentially by respectivecontrol circuits as illustrated in FIG. 14, this being effected byarranging the timing discs of each control system so that a givenmolding station will complete its operating cycle prior to operation ofthe next station in the sequence.

As an example, the operation of station 38 will be described. Whentiming disc 328 closes switch 342, solenoid 356 is energized to openvalve 358 and extend the piston rod passages 324 in valve body 156.Thus, the plastic will not foul the bearings 300 or 302 and may berecovered uncontaminated for reuse.

Gate 242 directs the flowing plastic stream into the space between heads206 and 208, whereupon divider ring 246 splits the stream into separatecomponents for ow through channels 230 and 252 of the heads. Since thechannels are etectively blocked by stops 236 and 258, respectively, theplastic flows toward these stops from the ends 238 of channel 230 andfrom the ends 260 of channel 252.

Ultimately, it will be appreciated that the plastic overflows thechannels and is discharged therefrom into the cylindrical passage aroundthe cylinder 204 of mandrel guide 202. Initially, the integrity of thetwo stream cornponents is maintained, since the upper stream isdischarged through annular opening 268, and the lower stream isdischarged through the annular portion of aperture 266 between flange248 and the internal surface of lower head 208. Thus, the two streamcomponents are discharged from the heads in the form of concentrictubular sheaths which unite as they ilow downwardly toward the orifice212.

Referring to FIG. 13, the composite tube formed upon unification of thetwo sheaths is there depicted. The outer sheath is designated 418, theinner sheath being designated 420. A weld line or seam 422 is shown insheath 418, a weld line or seam 424 being located in sheath 420 indiametric opposition to weld line 422. These weld lines are formed bythe webs or stops 236 and 258 of the heads which, as discussed above,divide each of the two flow channels into a pair of independentsegments. Since the two heads are located with the stops 236 and 258 indiametric opposition relative to the axis 9 of mandrel 196, it isevident that the weld lines 422 and 424 will bear a like relationship toone another.

The cam surfaces of timing discs 328 and 330 are so arranged that switch342 will be reopened just prior to closure of switch 344 by disc 330.This energizes solenoid 360 to open valve 362 and return the crank 160to the position shown. This closes the plastic control valve byreturning valve spool 286 to the position illustrated, andsimultaneously releases actuator 176 to operate hydraulic valve 178 andcommunicate lines 410 and 414. Line 416 is allowed to bleed throughoutlet 412 to the return line of the hydraulic system, and cylinder 180returns to the position shown.

After closure of the plastic control valve, timing disc 332 effectsclosure of switch 346 to energize solenoids 364 and 366 to open valves368 and 370. It will be appreciated that at this time, the compositeplastic tube is depending from orifice 212 between the die sections 144,which are separated from one another to receive the tube. Thus, openingof valves 368 and 370 shifts the die sections 144 toward one anotherinto engagement and traps the plastic tube therewithin.

Next, timing disc 334 closes switch 348 to energize solenoid 372 andopen valve 274. This permits air under pressure to pass through themandrel 196 and into the tube which is still in communication with themandrel air passage 264 since the tube has not as yet 1been separatedfrom oriiice 212. The blow molding operation is thus effected in theconventional manner, the air pressure within the plastic tube causingexpansion thereof and contact with the internal surfaces of the die. Theplastic is then permitted to cool and solidify.

Following solidication, timing disc 336 eiiects closure of switch 350 toenergize solenoid 376 and open exhaust valve 378.

Next, timing disc 338 operates switch 352 to energize solenoids 380 and382 which, in turn, open valves 384 and 370. Since valves 368 and 386have been reclosed, the pneumatic cylinders 150 are operated to separatethe die sections 144, leaving the iinished product suspended fromorifice 212.

Finally, timing disc 340 effects closure of switch 354 to energizesolenoid 288 and open valve 390 whereupon the single-acting pneumaticcylinder 224 momentarily extends its piston rod 225 to lower paddle 222land dislodge the plastic product for gravitation to a chute (notshown).

In the layout of the molding apparatus, it should be understood that thescheme represented by FIG. 1 is of signicance. The actual distancetraveled by the fluid plastic from homogenizer 24 to each of the moldingstations is the same, since the lengths of the secondary lines 34, 36,46, and 48 are staggered as shown. This is done so that the pressure ofthe fluid plastic mass at each station will be the same, therebyassuring uniformity of operation of the molding stations.

Additionally, those skilled in the art will appreciate that it isnecessary to maintain the plastic at an elevated temperature untilactual discharge thereof from the orifice 212. Thus, electric heatingelements (not shown) may be located along the various distribution linesand at the valve body and mandrel housing of each station.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. Means for extruding a composite plastic tube for subsequent blowmolding comprising: a pair of molding heads; means communicating withthe heads for direct,- ing a stream of plastic to be molded thereinto,said heads being provided with means for discharging said streamtherefrom in the form of a pair of tubular, relatively telescopedsheaths; and means for receiving said sheaths and extruding the sameinto a composite tube having a predetermined wall thickness.

2. The invention of claim 1, wherein said heads have means for formingweld lines in respective sheaths, the heads being disposed to dischargesaid sheaths with said weld lines out of alignment with one another,whereby to prevent the formation of a line of weakness through the wallof the composite tube.

3. Means for extruding a composite plastic tube for subsequent blowmolding comprising: au upper and a lo-wer molding head; meanscommunicating with the heads for directing plastic to be moldedthereinto, said lower head having an aperture therethrough and means fordischarging said -plastic through said aperture in the form of a tubularsheath, said upper head being provided with means defining an opening oflesser size than said aperture and aligned therewith, and means yfordischarging said plastic through said opening in the form of a tubularsheath, whereby the latter is contained within the sheath formed by saidlower head; and means below said heads for extruding said telescopedsheaths into a composite tube having a predetermined wall thickness.

4. The invention of claim 3, wherein the discharging means of each ofsaid heads includes structure for forming a weld line in the associatedsheath, the heads being disposed with said structures out of alignmentwith one another, whereby to prevent the formation of a line of weaknessthrough the wall of the composite tube.

5. Means for extruding a tube of plastic -material comprising anextrusion chamber and core means therein forming an annular extrusionpassage, annular means in said passage dividing the same into inner andouter an- -nular passages, means entering one side of said chamber forsupplying plastic material thereto whereby plastic flows around saidcore means in opposite circumferential directions and joins at the sidegenerally opposite to said supply means to form tubular conligurationsin said inner and outer annular passages, and means for retarding theiiow of plastic to one side of one of said annular passages to displacethe aforesaid joinder of plastic material therein circumferentiallywhereby the weld lines formed by said joinders in the inner and outerpassages are not coincident, and means for jointly extruding the tubularrformations of the inner and outer annular passages as a single tube.

References Cited UNITED STATES PATENTS 1,730,638 vlO/l929 Young 18-14 X2,171,095 8/1939 Orsini 18-14 3,404,432 10/1968 White et al. 18-13wiLBUR L. McBAY, Primary Examiner

